In situ tunable pillaring of compact and high-density graphite fluoride with pseudocapacitive diamines for supercapacitors with combined predominance in gravimetric and volumetric performances

Abstract

For most graphene electrodes, there is usually a disappointing trade-off relationship between gravimetric and volumetric capacitive characteristics, which is definitely a major stumbling block in the development of real-life supercapacitors with high energy density. Herein, we rationally designed a hierarchically porous and modestly packed diamine pillared graphene, which is achieved by a facile and straightforward reaction between commercialized bulk graphite fluoride and in situ generated diamine anions. Combined reliable characterization studies demonstrate that an advantageous reductive defluorination of the unsubstituted carbon–fluorine units (C–F_x) accompanies the foreseen substitution of C–F_x by diamines, endowing the resultant products with recovered 2D π-conjugation and high conductivity. In comparison to ethylenediamine and p-phenylenediamine, pseudocapacitive 4,4′-oxydianiline (ODA) molecular pillars, having a bulky and rigid geometry, provide the ODA-G product with a greatly widened d-spacing (6.2 Å), large wettable and electrolyte-accessible specific surface area (1985 m² g⁻¹), hierarchically porous and interconnected structuration, heavyweight nature (density of 1.08 g cm⁻³), etc. Consequently, the symmetric supercapacitor fabricated using ODA-G as both electrodes delivers an impressive gravimetric capacitance of 328.5 F g⁻¹ and a maximized volumetric capacitance of 354.8 F cm⁻³ at a current density of 0.5 A g⁻¹, whilst exhibiting a remarkable rate capability and cycling stability. Apart from an exceptional gravimetric energy density, the volumetric energy density of the ODA-G device is as high as 19.5 W h L⁻¹ at a large power density of 9093 W L⁻¹. It is notable that this contribution deepens our insight into the chemistry of graphite fluoride, and can guide the judicious design and synthesis of versatile functionalized graphene applicable to other electrochemical energy-storage systems, or the newly-emerging photothermal water evaporation, desalination, etc.